This invention relates generally to the steering of the various sections of mobile articulated machines, and particularly to the steering of a section that is steered as a robot by a non-human control system. The preferred embodiments of the invention demonstrate a way of applying the principles of the invention to over-the-road tractor-trailer combinations. A driver controls the steering of a lead tractor, which carries the first trailer.
Over-the-road transport companies find it difficult at times to compete with other freight haulers due to labor costs. Labor costs could be decreased if each tractor-trailer rig could carry more weight, but weight limits have been placed on roads and bridges for structural reasons. Multi-trailer arrangements have been seen as a possible solution to this problem because they spread the load over a longer stretch of pavement and reduce the columnar loading on bridges. These arrangements generally involve long combination vehicles, a semi-trailer carried by the tractor with one or more full trailers composed of semi-trailers carried by dollies, called xe2x80x9cdoublesxe2x80x9d and xe2x80x9ctriplesxe2x80x9d.
These long combination vehicles face the two interconnected problems of instability and lack of maneuverability, with each following dolly (with trailer attached) becoming less stable at speed and, also, each following dolly xe2x80x9ccutting the cornerxe2x80x9d more than the vehicle segment in front of it during cornering. The standard Type A dolly has achieved some degree of success over the years by striking a point between the two problems. It hitches to the towing vehicle or first trailer using a single point hitch. The standard Type A dolly provides steering for the trailer it is carrying by allowing the entire dolly to steer relative to its semi-trailer about the fifth wheel vertical axis on the dolly as well as relative to the towing trailer about the single point hitch vertical axis. The dolly tires however, do not steer relative to the dolly frame.
Commercial vehicles of either truck and full trailer or multi-trailer configurations which employ the standard Type A dollies generally possess undesirable characteristics such as limited maneuverability and instabilities caused by rearward amplification. Rearward amplification, sometimes described as a crack-the-whip phenomenon, implies that in rapid evasive maneuvers such as emergency lane changes, the rearward elements of the vehicle train such as the dolly and the trailer carried by the dolly experience motions which are substantially amplified compared to the motions of the towing tractor and first trailer. Rearward amplification is known to be the basic cause of many accidents in which roll over of the last trailer or second trailer occurs while the remaining elements of the vehicle remain unscathed.
A second general class of dollies known as Type B dollies represents an improvement over standard Type A dollies. Type B dollies are generally characterized by a double tow bar arrangement, which eliminates steering of the dolly with respect to the towing vehicle, most commonly the first trailer. The Type B dollies have been effective to a degree against some of the instability problems and are slightly more maneuverable than the standard Type A dollies. However, they cause other problems such as introducing other types of instabilities, causing stresses on the rear of the forward trailer, and increasing unloading delays due to difficulty in accessing the back of the forward trailer for some configurations.
Steerable Type A dollies address the stability problems, but are even less maneuverable than Standard Type A dollies.
The long dolly of provisional patent No. 60/204,513 addressed these problems by switching between a stability and a cornering or maneuverability mode. The application of drive power to the dolly axles, provisional patent Ser. No. 09/776,211 did not change the steering but did allow the long dolly (with its trailer attached) to swing wider around a corner in the path dictated by steering modes that demanded a closer emulation of the behavior of the tractor.
Although an improvement, these modes of steering for the long dollies, stability and cornering, did not truly track the path of the tractor, but only traced a path that represented a typical expected path for a given maneuver. Clearly a mode of steering is needed for these long combination vehicles that would ensure that the following vehicle tracked the path of the forward vehicle as closely as possible, especially during critical cornering maneuvers in tight places.
A similar problem exists in narrow city streets where equipment must be delivered to an emergency site such as a fire, or where the delivery of other materials is required. A sectioned vehicle in which each short section followed the path of the first section would be better able to negotiate such streets than a single long vehicle. Similarly, in a convoy of RV""s traveling together, each vehicle requires a driver. If a mode of path tracking steering existed which would assure that successive vehicles followed the same path as the lead vehicle, a single driver might steer a convoy of several vehicles.
The present invention advances the concept of a robotic vehicle that is capable of tracking the path of a lead vehicle. At this point the device can no longer be considered a mere dolly but must more properly be called a robotic vehicle or robotic tractor, because it is fully capable of steering itself in response to input and of propelling itself during cornering. It is also capable of selecting other desired steering modes, including, for example, a mode in which the stability is enhanced at a slight expense to its tracking capability.
The details of this robotic tractor include mathematical equations and algorithms, electronic hardware, and a mechanical system.
It is an objective of this invention to advance the concept of a robotic vehicle that is capable of tracking the path of a lead vehicle, and that is fully capable of steering itself in response to input, of propelling itself during cornering, and of selecting other desired steering modes, including, for example, a mode in which the stability is enhanced at a slight expense to its tracking capability.
It is an objective of this invention to present a mathematical model that would allow a multiplicity of path-tracking and non-path-tracking steering algorithms to be combined in a coherent manner using a variety of weighting factors, and to point toward even more complex control algorithms.
It is an objective of this invention to provide a plurality of mathematical algorithms based on physical principles and on the geometry of the vehicle configurations, each of which is compatible with the above system for combining algorithms, for steering a robotic vehicle to track the path of a lead vehicle.
It is an objective of this invention to present an electronic control system, preferably including hardware such as sensors, actuators, and other I/O devices, RAM, ROM, and other data storage devices, and digital processors, that is capable of acquiring data from these sensors, using that data as input to algorithms to generate control signals, and using these control signals to activate steering and other control components to enable a robotic vehicle to track the path of a lead vehicle.
It is an objective of this invention to present a mechanical system that is capable of being controlled by the actuators to track the path of the lead vehicle, thereby eliminating the need for a second operator for the second vehicle.
The first advantage of this invention is the increase in maneuverability for shorter sectioned delivery or emergency vehicles in places such as narrow city streets. The long wheelbases of standard trucks and tractor-trailer combinations cause them to xe2x80x9ccut the cornerxe2x80x9d during turns. In narrow city streets such as those found in many European cities, this behavior could be disastrous. A vehicle composed of a number of shorter sections that were steered so that each section tracked the first section could solve some of the problems in these types of situations.
Another advantage of this invention is the savings in labor costs in applications such as over-the-road freight transport. The length of the robotic tractor spreads the load and permits more weight to be carried by a single long combination vehicle driven by a single driver. A robotic tractor xe2x80x9cdoublexe2x80x9d eliminates one driver, and a robotic tractor xe2x80x9ctriplexe2x80x9d eliminates two drivers. At the same time, because of the ability of the robotic tractor(s) to track the path of the lead tractor while carrying its own trailer, the loss of maneuverability is minimal. Because of the length and because of the capability for using a more stable mode at higher speeds, there is also no appreciable loss of stability as compared to a single tractor-trailer rig.
Another advantage of this invention is that it requires minimal supervision from the driver. The controller is programmed to steer using input from its sensors (such as speed of travel or quickness of a turn), and by taking clues from the normal control activities of the driver. To set up the long combination vehicle, the driver has only to adjust the length of the tongue and input the length of the tractor and the trailers.
Another advantage of this invention is that the robotic tractor embodiment can carry standard semi-trailers with only very minor modifications. Standard tractors could also be used as lead tractors with only slightly more substantial modifications, such as the addition of the appropriate sensors.
This invention offers the stability of the steerable Type A dollies but with better cornering capabilities than the Type B dolly. It also takes advantage of the reduction in cost and the rapid growth in the capabilities of electronic computing hardware.